Standard deviation help please

I am sorry that I am asking this question as I'm sure that this is very simple for people on this site but I'm a Masters student who has not taken Linear equations before and have questions and am having a hard time with a problem, here it is:

A study was conducted involving 20 young children. the mean age of the children was 4.0 years, and the standard deviation was 1.2 years. A colleague recommends that age be reported in months rather than years. What is the standard deviation when the childrens age is expressed in months rather than years?

I am sorry that I am asking this question as I'm sure that this is very simple for people on this site but I'm a Masters student who has not taken Linear equations before and have questions and am having a hard time with a problem, here it is:

A study was conducted involving 20 young children. the mean age of the children was 4.0 years, and the standard deviation was 1.2 years. A colleague recommends that age be reported in months rather than years. What is the standard deviation when the childrens age is expressed in months rather than years?

Let Y = aX + b.

Then E(Y) = a E(X) + b, Var(Y) = a^2 Var(X) and sd(Y) = |a| sd(X).

Your job is to get a relationship between X (age measured in years) and Y (age measured in months) and then get sd(Y).